1. Field of the Invention
The present invention relates to a vapor-phase method of synthesizing diamond, and more particularly relates to a vapor-phase method employing a combustion flame. The diamond produced by this method is suitable for numerous applications including use as semiconductor elements requiring high purity, high crystallinity, high heat conductivity, low dielectricity, high light-transmissivity, high anelasticity, high strength, high abrasion resistance, high-durability, and high-temperature operability. Advantages of use of the present method include inexpensive synthesis, high-speed production, and stability of the synthesis operation.
2Description of the Related Art
Conventionally, artificial diamond has been synthesized in a thermodynamic equilibrium under high temperature and high pressure. Recently, however, it has become possible to synthesize diamond in the vapor phase. In the vapor-phase synthesis method, hydrocarbon gas diluted with ten times or more hydrogen is excited in a reaction chamber by means of plasma or a heat filament to form a diamond layer on a basic material. In this method, however, the evaporation speed of 0.1-2 .mu.m/h is so low as to render the method unsuitable for industrial use.
In the 35th Applied Physics Related Joint Lecture Meeting (April 1988), Hirose, et al. of Nippon Kodai reported that diamond could be synthesized by use of a combustion flame.
Further, in New Diamond, Vol. 4, No. 3, pp. 34-35, a diamond synthesis method employing a combustion flame has been disclosed.
Synthesis of diamond in the vapor phase by means of a combustion flame is such a new process, however, that suitable synthesis conditions have heretofore not been discovered. Numerous problems have been encountered in the prior art in providing a diamond of acceptable reproducibility and crystallinity, with an industrially-acceptable rate of film growth, while simultaneously ensuring the process stability necessary for long-duration synthesis.
More specifically, the vapor-phase combustion method, as opposed to conventional vapor-phase synthesis, produces super saturation of the carbon material. As a result, surface graphitization and surface amorphousization occur, inhibiting the deposition of a diamond of the desired crystallinity. This limits the synthesis run length during which stable operation can be expected to a commercially-infeasible period of less than several hours.